1. Field
The present disclosure is directed to additive compositions and lubricants containing acyl N-methyl glycines and derivatives thereof. In particular, it is directed to additive compositions and engine oils containing acyl N-methyl glycines and derivatives thereof in combination with one or more metal dialkyl dithio phosphate salt(s).
2. Description of the Related Technology
To ensure smooth operation of engines, engine oils play an important role in lubricating a variety of sliding parts in the engine, for example, piston rings/cylinder liners, bearings of crankshafts and connecting rods, valve mechanisms including cams and valve lifters, and the like. Engine oils may also play a role in cooling the inside of an engine and dispersing combustion products. Further possible functions of engine oils may include preventing or reducing rust and corrosion.
The principle consideration for engine oils is to prevent wear and seizure of parts in the engine. Lubricated engine parts are mostly in a state of fluid lubrication, but valve systems and top and bottom dead centers of pistons are likely to be in a state of boundary and/or thin-film lubrication. The friction between these parts in the engine may cause significant energy losses and thereby reduce fuel efficiency. Many types of friction modifiers have been used in engine oils to decrease frictional energy losses.
Improved fuel efficiency may be achieved when friction between engine parts is reduced. Thin-film friction is the friction generated by a fluid, such as a lubricant, moving between two surfaces, when the distance between the two surfaces is very small. It is known that some additives normally present in engine oils form films of different thicknesses, which can have an effect on thin-film friction. Some additives, such as zinc dialkyl dithio phosphate (ZDDP) are known to increase thin-film friction. Though such additives may be required for other reasons such as to protect engine parts, the increase in thin-film friction caused by such additives can be detrimental.
Reducing boundary layer friction in engines may also enhance fuel efficiency. The motion of contacting surfaces in an engine may be retarded by boundary layer friction. Non-nitrogen-containing, nitrogen-containing, and molybdenum-containing friction modifiers are sometimes used to reduce boundary layer friction.
U.S. Pat. No. 5,599,779 discloses a lubricant composition containing a three component rust inhibitor package including a compound of the formula:
and an amine salt of a dicarboxylic acid. Here R represents a C8-18-alkyl or alkenyl group. The amine salt of a dicarboxylic acid is prepared by formulating the rust inhibitor package to contain about one mole of a compound having the structural formula:HOOC(CH2)XCOOHwherein x is an integer from 4 to 46 and about 2 moles of an amine selected from compounds having the formula:
wherein R1, R2, and R3 are independently selected from hydrogen, alkyl having up to 14 carbon atoms, hydroxyalkyl, cycloalkyl, or polyalkyleneoxy groups. The rust inhibitor package may be used in lubricant compositions formulated with crankcase and diesel oils.
WO 2009/140108 discloses the use of a variety of different rust inhibiting compounds for certain types of multifunctional oils. In the specification there is a brief mention of the possibility of using a compound of the formula:
wherein R and R1 are not defined. No further details are given as to the amounts that should be used, nor are any specific formulations including such compounds exemplified in the application.
GB 1 235 896 discloses multifunctional lubricants and includes an example of a wet brake formulation including oleyl sarcosine. The exemplified composition also includes basic calcium sulphonate detergent (TBN=300), P2S5-polybutene barium phenate/sulphonate detergent, a dispersant that is a reaction product of polybutenyl succinic anhydride with an Mw=900 PIB group and tetraethylene pentamine, zinc dihexyl dithiophosphate, dioleyl phosphite, sperm oil, and sulphurised polybutene.
The metal salts of dialkyl dithio phosphates are often used in lubricants as anti-wear agents. One example of such use is found in U.S. Pat. No. 8,084,403. However, use of these additives may alter the friction characteristics of the lubricants.
In recent years there has been a growing desire to employ lubricants that provide higher energy-efficiency, especially lubricants that reduce friction. Also, there is a desire to provide improved additive combinations that achieve multiple goals while still providing the desired performance levels.